Can my vote be altered?

No. Illegally changing votes would require a conspiracy of unscrupulous voters or election insiders, or a combination of the two. The electoral process is designed in such a way that no single individual, or even a small group of individuals, can tamper with the election results. It is also important to note that such a conspiracy would not necessarily require any "security relevant flaws" in the software code to accomplish its aims. Fraud of this degree would have the potential to undermine any voting system.